Energy-efficient window coatings transmissible to wireless communication signals and methods of fabricating thereof

ABSTRACT

Provided are novel energy-efficient signal-transparent window assemblies and methods of fabricating thereof. These window assemblies are specifically configured to allow selective penetration of electromagnetic wavelengths greater than 0.5 millimeters, representing current and future wireless signal spectrum. This signal penetration is provided while IR-blocking properties are retained. Furthermore, the window assemblies remain substantially transparent within the visible spectrum with no specific features detectable to the naked eye. This unique performance is achieved by patterning conductive layers such that the conductive layer edges remain protected during most fabrication steps and the fabrication. As such, the conductive layers are encapsulated and separated from the environment while retaining separation between individual disjoined structures of these layers. For example, a barrier layer and/or a dielectric layer may extend over the conductive layer edge. The patterning is achieved by forming photoresist structures on the substrate and depositing a low-E stack over these photoresist structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/198,796, filed on 2021 Mar. 11, which claims the benefit under 35U.S.C. § 119(e) of U.S. Provisional Patent Application 62/988,268, filedon 2020 Mar. 11, and also of U.S. Provisional Patent Application63/027,111, filed on 2020 May 19, all of which are incorporated hereinby reference in their entirety for all purposes.

BACKGROUND

Windows tend to be the least energy-efficient component in buildings.For example, radiation-based heat transfer represents about 60% of thetotal energy loss through standard windows. Energy-efficient windowsutilize special coatings to reduce this heat transfer, e.g., by blockingthe IR (infrared) radiation, corresponding to wavelengths between 5micrometers to 50 micrometers. However, energy-efficient windows alsotend to block wireless communication signals with wavelengths longerthan 50 micrometers or even longer than 0.5 millimeters. This signalblocking negatively impacts cellular reception, Wi-Fi access, and thelike. Conventional approaches use external antennas to rebroadcastsignals inside the building. However, such systems are complex,expensive, and provide minimal coverage inside the buildings.Furthermore, covering all areas inside the building with such systemscan be difficult.

SUMMARY

Provided are novel energy-efficient signal-transparent window assembliesand methods of fabricating thereof. These window assemblies arespecifically configured to allow selective penetration of millimeterwaves, representing current and future wireless signal spectrums. Thissignal penetration is provided while IR-blocking properties areretained. Furthermore, the window assemblies remain substantiallytransparent within the visible spectrum with no specific featuresdetectable to the naked eye. This unique performance is achieved bypatterning conductive layers such that the conductive layer edges remainprotected during most fabrication steps and the fabrication. As such,the conductive layers are encapsulated and separated from theenvironment while retaining separation between individual disjoinedstructures of these layers. For example, a barrier layer and/or adielectric layer may extend over the conductive layer edge. Thepatterning is achieved by forming photoresist structures on thesubstrate and depositing a low-E stack over these photoresiststructures.

In some examples, an energy-efficient signal-transparent window assemblycomprises a window substrate, non-conductive spacers, a first dielectriclayer, a conductive layer, a barrier layer, and a second dielectriclayer. The non-conductive spacers form a pattern on the windowsubstrate, interfacing a portion of the window substrate, and blockingthe portion of the window substrate. The first dielectric layerinterfaces the window substrate and the non-conductive spacers. Theconductive layer is disposed over the first dielectric layer such thatthe first dielectric layer is disposed between the conductive layer andeach of the window substrate and the non-conductive spacers. Theconductive layer is formed by multiple disjoined structures defined bythe pattern of the non-conductive spacers. The barrier layer is disposedover the conductive layer such that the conductive layer is disposedbetween the first dielectric layer and the barrier layer. The seconddielectric layer is disposed over the barrier layer such that thebarrier layer is positioned between the second dielectric layer and theconductive layer, such that the first dielectric layer, the conductivelayer, the barrier layer, and the second dielectric layer form a stackat least over a portion of the window substrate. Each of the firstdielectric layer and the second dielectric layer is either a uniformmonolithic structure or a multi-layered structure.

In some examples, the non-conductive spacers comprise at least one ofphotoresist, fibers, wires, and transparent material. For example, thenon-conductive spacers comprise a positive photoresist.

In some examples, the first dielectric layer, the conductive layer, thebarrier layer, and the second dielectric layer formsubstrate-interfacing stacks and spacer-interfacing stacks. Each of thesubstrate-interfacing stacks interfaces the window substrate and ispositioned between two adjacent ones of the non-conductive spacers. Thespacer-interfacing stacks are positioned such that the non-conductivespacers are disposed between the spacer-interfacing stacks and thewindow substrate. The substrate-interfacing stacks may be disjoined fromthe spacer-interfacing stacks. In some examples, the non-conductivespacers protrude between and above the substrate-interfacing stacks. Forexample, the non-conductive spacers have a height at least greater thanthe height of the substrate-interfacing stacks.

In some examples, each of the non-conductive spacers has asubstrate-interfacing surface and a dielectric-interfacing surface,opposite of the substrate-interfacing surface. The width of thedielectric-interfacing surface is larger than the width of thesubstrate-interfacing surface. For example, the difference between thewidth of the dielectric-interfacing surface and the width of thesubstrate-interfacing surface is at least 100 nanometers.

In some examples, each of the non-conductive spacers comprises a spacerbase and a spacer head. The spacer base defines the first spacersurface. The spacer head defines the second spacer surface and is formedfrom a material different than the spacer base.

In some examples, each of the non-conductive spacers is disposed betweentwo adjacent sidewalls, each extending to the window substrate andformed by at least one of the barrier layer and the second dielectriclayer. For example, each of the two adjacent sidewalls is formed atleast by both the barrier layer and the second dielectric layer. In someexamples, each of the two adjacent sidewalls has a sidewall surface,facing a corresponding one of the non-conductive spacers. The sidewallsurface is separated from the conductive layer by at least 2 nanometers.

In some examples, the first dielectric layer, the conductive layer, thebarrier layer, and the second dielectric layer formsubstrate-interfacing stacks and spacer-interfacing stacks. Each of thesubstrate-interfacing stacks and spacer-interfacing stacks is covered byone or more additional stacks, each comprising the first dielectriclayer, the conductive layer, the barrier layer, and the seconddielectric layer.

In some examples, the energy-efficient signal-transparent windowassembly further comprises a patterned portion and a non-patternedportion. The conductive layer is formed by the multiple disjoinedstructures in the patterned portion. The conductive layer is acontinuous structure in the non-patterned portion.

In some examples, an energy-efficient signal-transparent window assemblycomprises a window substrate, a first dielectric layer, a conductivelayer, a barrier layer, and a second dielectric layer. The firstdielectric layer is disposed over the window substrate. The conductivelayer is disposed over the first dielectric layer such that the firstdielectric layer is disposed between the conductive layer and the windowsubstrate. The conductive layer is formed by multiple disjoinedstructures defined by openings forming a pattern, wherein each of theopenings is disposed between two adjacent sidewalls. The barrier layeris disposed over the conductive layer such that the conductive layer isdisposed between the first dielectric layer and the barrier layer. Thesecond dielectric layer is disposed over the barrier layer such that thebarrier layer is positioned between the second dielectric layer and theconductive layer. The first dielectric layer, the conductive layer, thebarrier layer, and the second dielectric layer form asubstrate-interfacing stack at least over a portion of the windowsubstrate. Each of the two adjacent sidewalls extends to the windowsubstrate and is formed by at least one of the barrier layer and thesecond dielectric layer. Each of the first dielectric layer and thesecond dielectric layer is either a uniform monolithic structure or amulti-layered structure.

In some examples, a portion of the window substrate between the twoadjacent sidewalls is exposed. For example, the portion of the windowsubstrate between the two adjacent sidewalls is planar and substantiallyintact. In some examples, each of the two adjacent sidewalls is formedat least by both the barrier layer and the second dielectric layer.

In some examples, each of the two adjacent sidewalls has a sidewallsurface, facing another of the two adjacent sidewalls. The sidewallsurface is separated from the conductive layer by at least 2 nanometers.

In some examples, a method of forming an energy-efficientsignal-transparent window assembly comprises forming a pattern ofnon-conductive spacers on a window substrate. The method proceeds withdepositing a stack over the window substrate and the non-conductivespacers. The stack comprises a first dielectric layer, a conductivelayer, a barrier layer, and a second dielectric layer. The conductivelayer comprises multiple disjoined structures defined by the pattern ofthe non-conductive spacers.

In some examples, the pattern of the non-conductive spacers is formedusing at least one of (a) photolithography, such that the non-conductivespacers comprise photoresist, (b) imprint lithography, and (c)mechanical placement of the non-conductive spacers. Furthermore, in someexamples, forming the pattern of the non-conductive spacers comprisesforming undercuts in the non-conductive spacers, such that each of thenon-conductive spacers has a substrate-interfacing surface and adielectric-interfacing surface, opposite of the substrate-interfacingsurface and such that a width of the dielectric-interfacing surface is alarger than a width of the substrate-interfacing surface.

In some examples, each of the non-conductive spacers comprises a spacerbase and a spacer head such that the spacer base and the spacer head areformed from different materials having different etching rates. Theundercuts are formed due to the different etching rates of the spacerbase and the spacer head.

In some examples, the method further comprises tempering theenergy-efficient signal-transparent window assembly such that thenon-conductive spacers are removed during tempering. In some examples,depositing the stack comprises forming two adjacent sidewalls aroundeach of the non-conductive spacers such that each of the two adjacentsidewalls extends to the window substrate and is formed by at least oneof the barrier layer and the second dielectric layer.

These and other examples are described further below with reference tothe figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-sectional view of an energy-efficientsignal-transparent window assembly, comprising non-conductive spacersand low-E stacks positioned at different levels relative to the windowsubstrate, in accordance with some examples.

FIG. 1B is a schematic expanded view of a portion of theenergy-efficient signal-transparent window assembly in FIG. 1A.

FIG. 1C is a schematic cross-sectional view of another example of theenergy-efficient signal-transparent window assembly, comprisingnon-conductive spacers formed from two layers.

FIG. 1D is a schematic cross-sectional view of another example of theenergy-efficient signal-transparent window assembly, in which thenon-conductive spacers formed are wires disposed over the windowsubstrate.

FIG. 1E is a schematic cross-sectional view of another example of theenergy-efficient signal-transparent window assembly comprising aprotective layer.

FIG. 2A is a schematic cross-sectional view of an energy-efficientsignal-transparent window assembly with substrate-interface low-E stacksand no spacers, in accordance with some examples.

FIG. 2B is a schematic cross-sectional view of an energy-efficientsignal-transparent window assembly formed using conventional methods,such as laser scribing.

FIG. 3 is a schematic cross-sectional view of an energy-efficientsignal-transparent window assembly with multiple low-E stacks formed ontop of each other, in accordance with some examples.

FIG. 4A is a schematic top view of an energy-efficientsignal-transparent window assembly, showing one pattern example.

FIG. 4B is a schematic top view of an energy-efficientsignal-transparent window assembly, showing another pattern example.

FIG. 4C is a schematic top view of an energy-efficientsignal-transparent window assembly, showing patterned portions andnon-patterned portions.

FIG. 5 is a process flowchart of a method for forming anenergy-efficient signal-transparent window assembly, in accordance withsome examples.

FIGS. 6A-6D are schematic cross-sectional views of various stages of themethod while forming an energy-efficient signal-transparent windowassembly, in accordance with some examples.

FIGS. 6A-6D are schematic cross-sectional views of various stages of themethod while forming non-conductive spacers of an energy-efficientsignal-transparent window assembly, in accordance with some examples.

FIG. 6E is a schematic cross-sectional view of a non-conductive spacer,showing an undercut, in accordance with some examples.

FIGS. 7A-7D are schematic views of other methods of formingnon-conductive spacers of an energy-efficient signal-transparent windowassembly, in accordance with some examples.

FIGS. 8A-8D are schematic cross-sectional views of various stages of themethod while forming a low-E stack over a non-conductive spacer andwindow substrate, in accordance with some examples.

FIG. 9 illustrates the results of the Wi-Fi signal penetration test.

DETAILED DESCRIPTION

In the following description, numerous specific details are outlined inorder to provide a thorough understanding of the presented concepts. Thepresented concepts may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the describedconcepts. While some concepts will be described in conjunction with thespecific embodiments, it will be understood that these embodiments arenot intended to be limiting.

INTRODUCTION

Energy-efficient windows are becoming more popular in commercial andresidential buildings as well as in other applications. Anenergy-efficient window may comprise one or more silver-based layers,responsible for blocking IR radiation, in addition to various dielectriclayers and barrier layers. These silver-based layers may be alsoreferred to as metal layers or conductive layers. However,energy-efficient windows or, more specifically, silver-based layers tendto interfere with the wireless signal transmission (e.g., cellularsignal) due to signal attenuation. As noted above, conventionalsolutions involve the installation of distributed antenna systems (DAS)within buildings to promote signal propagation. However, this approachrequires special equipment, additional power consumption, and additionalcost.

It has been found that using separating a conductive layer into multipledisjoined structures helps to reduce signal attenuation. It should benoted that the wavelength of electromagnetic waves, which can passthrough this patterned conductive layer, depends on the opening sizebetween the disjoined structures. More specifically, the wavelengthdepends on the opening width between pairs of adjacent disjoinedstructures, e.g., the largest opening width is smaller than thewavelength. For example, a continuous conductive layer may be formedover the substrate and subsequently patterned, e.g., removing smallportions of this conductive layer and forming top-to-bottom/throughopenings (e.g., extending to the substrate). However, the patterningprocess and subsequent exposure of conductive layer edges (within theopenings) cause various durability issues with these silver-basedconductive layers as well as aesthetics issues (e.g., unsightly visibleline marks). As a result, patterning methods have not been widelyadopted. Furthermore, patterning becomes very challenging when dealingwith the 5^(th) generation (5G) networks using wavelengths greater than1 millimeter. Such wavelengths require openings smaller than 0.1millimeters in width to achieve adequate signal transmission. Futuregeneration networks are expected to use even shorter wavelengthsrequiring smaller openings, which may be challenging to achieve withconventional laser scribing techniques.

Described herein are various examples of energy-efficientsignal-transparent window assemblies and methods of fabricating thereof.These assemblies are transparent in the visible light region, allowingpenetration of the electromagnetic waves at set wavelengths (e.g.,carrying wireless communication signals), and are configured to blockthe IR radiation. For example, the transparency in the visible lightregion (e.g., wavelength 350-800 nanometers) may be between 10% and 100%transmission. In the same or other examples, the energy-efficientsignal-transparent window assemblies allow penetration of theelectromagnetic waves having a wavelength of 12.5 centimeters(corresponding to 2.4 GHz frequency) at only around 5 dB extra loss thanthat of an uncoated window substrate. Furthermore, theIR-blocking/emissivity is less than 0.15 in some examples. This valueindicates that more than 85% of spectra between wavelength 5 micrometersto 50 micrometers is blocked by an energy-efficient signal-transparentwindow assembly. For comparison, conventional low-E windows (e.g., asample from AGC Glass North America Alpharetta, Ga.) reported around 30DB signal loss measured from 1 GHz to 5 GHz.

Furthermore, the energy-efficient signal-transparent window assembliesdescribed herein do not have unsightly visible marks and have a pleasantaesthetic appearance, unlike laser-patterned low-E windows. For example,when a window assembly is inspected at an angle of 90° to its surfacewith a uniform backlight simulating daylight (e.g., light intensity10,000 lux or above), no visible marks can be observed withoutmagnification (i.e., not observable with the “naked eye”). Furthermore,a digital photo, with a pixel density of 150,000 pixels percentimeter-square also does not show any visible marks.

The energy-efficient signal-transparent window assemblies describedherein also have long-term durability. For example, an accelerateddurability test, which involves dipping a sample into boiling water forone hour, does not reveal any visible marks with the inspection criteriapresented above (e.g., the “naked eye” inspection and digital photo).Furthermore, no additional defects, which are attributable to thisaccelerated durability test, were detected under the microscope. Anotheraccelerated durability was performed by baking a sample in a 650° C.oven for 8 minutes. Likewise, the microscope inspection did not revealany additional defects.

Finally, the energy-efficient signal-transparent window assemblies allowwireless signal propagation of 5G signals (frequency of 6 GHzcorresponding to 50-millimeter wavelength) and other like signals (e.g.,future generation using higher frequencies and smaller wavelengths). Insome examples, the opening width is 0.1 millimeters or even less, whichmuch smaller than the wavelength of these communication technologies.

Examples of Energy-Efficient Signal-Transparent Window Assemblies

FIG. 1A illustrates one example of energy-efficient signal-transparentwindow assembly 100, comprising window substrate 110, first dielectriclayer 120, conductive layer 130, barrier layer 140, and seconddielectric layer 150. In this example, energy-efficientsignal-transparent window assembly 100 also comprises non-conductivespacers 180, which forms pattern 185 on window substrate 110. Variousexamples of pattern 185 are described below with reference to FIGS. 4Aand 4B. Non-conductive spacers 180 interface a portion of windowsubstrate 110 and block this portion of window substrate 110.

First dielectric layer 120 is disposed over window substrate 110 andnon-conductive spacers 180. More specifically, a first portion of firstdielectric layer 120 interfaces window substrate 110, while a secondportion of first dielectric layer 120 interfaces non-conductive spacers180. In this example, non-conductive spacers 180 are positioned betweenthe second portion of first dielectric layer 120 and window substrate110 thereby separating the second portion of first dielectric layer 120from window substrate 110. As such, the first portion of firstdielectric layer 120 and the second portion of first dielectric layer120 are not so-planar. Instead, the first portion of first dielectriclayer 120 and the second portion of first dielectric layer 120 areoffset from each other by the height (along the Z-axis) ofnon-conductive spacers 180. Furthermore, in some examples, the firstportion of first dielectric layer 120 is disjoined from the secondportion of first dielectric layer 120. In other words, the first portionof first dielectric layer 120 does not directly contact the secondportion of first dielectric layer 120.

Conductive layer 130 is disposed over first dielectric layer 120 suchthat first dielectric layer 120 is positioned between conductive layer130 and each of window substrate 110 and non-conductive spacers 180.Conductive layer 130 is formed by multiple disjoined structures 132,defined by pattern 185 of non-conductive spacers 180. For example, afirst set of multiple disjoined structures 132 are disposed over thefirst portion of first dielectric layer 120, which interfaces windowsubstrate 110. A second set of multiple disjoined structures 132 aredisposed over the second portion of first dielectric layer 120, whichinterfaces non-conductive spacers 180. As with the first and secondportions of first dielectric layer 120, the first and second sets ofmultiple disjoined structures 132 are non-planar and are offset fromeach other by the height (along the Z-axis) of non-conductive spacers180. It should be noted that multiple disjoined structures 132 allowstransmission of electromagnetic waves through energy-efficientsignal-transparent window assembly 100 as noted above.

Barrier layer 140 is disposed over conductive layer 130 such thatconductive layer 130 is disposed between first dielectric layer 120 andbarrier layer 140. Similar to first dielectric layer 120 and conductivelayer 130, in some examples, barrier layer 140 comprises a first portionand a second portion. The first portion of barrier layer 140 is disposedover the first set of multiple disjoined structures 132, which aredisposed over the first portion of first dielectric layer 120, whichinterfaces window substrate 110. The second portion of barrier layer 140is disposed over the second set of multiple disjoined structures 132,which are disposed over the second portion of first dielectric layer120, which interfaces non-conductive spacers 180.

Finally, second dielectric layer 150 is disposed over barrier layer 140such that barrier layer 140 is positioned between second dielectriclayer 150 and conductive layer 130. Similar to other components ofenergy-efficient signal-transparent window assembly 100, seconddielectric layer 150 comprises a first portion and a second portion. Thefirst portion of second dielectric layer 150 is disposed over the firstportion of barrier layer 140. The second portion of second dielectriclayer 150 is disposed over the second portion of barrier layer 140.

As such, first dielectric layer 120, conductive layer 130, barrier layer140, and second dielectric layer 150 collectively form different typesof stacks over window substrate 110, which may be referred to assubstrate-interfacing stacks 171 and spacer-interfacing stacks 172.Substrate-interfacing stacks 171 is formed by the first portion of firstdielectric layer 120, the first set of multiple disjoined structures132, the first portion of barrier layer 140, and the first portion ofsecond dielectric layer 150. As noted above, the first portion of firstdielectric layer 120 interfaces window substrate 110. Spacer-interfacingstacks 172 are formed by the second portion of first dielectric layer120, the second set of multiple disjoined structures 132, the secondportion of barrier layer 140, and the second portion of seconddielectric layer 150. As noted above, the second portion of firstdielectric layer 120 interfaces non-conductive spacers 180. The numberof these stacks depend on pattern 185 formed by non-conductive spacers180. For example, each of non-conductive spacers 180 may have one of thecorresponding spacer-interfacing stacks 172, disposed over that spacer,and two substrate-interfacing stacks 171, disposed on each side of thatspacer.

The composition and other structural features of each component will notbe described in more detail. In some examples, window substrate 110comprises glass, plastics, or any materials that can support at leastfirst dielectric layer 120, conductive layer 130, barrier layer 140, andsecond dielectric layer 150. In some examples, window substrate 110 istransparent.

In some examples, first dielectric layer 120 and second dielectric layer150 are formed from the same material. Alternatively, first dielectriclayer 120 and second dielectric layer 150 are formed from differentmaterials. In general, materials suitable for first dielectric layer 120and second dielectric layer 150 include, but are not limited to,transparent dielectric materials such as a zin-tin oxide(Zn_(x)Sn_(y)O_(z)) and a silicon nitride (Si₃N₄). In some examples, thedielectric conductivity of the material forming first dielectric layer120 and/or second dielectric layer 150 is smaller than 1000 S/M (Siemensper meter) or, more specifically, smaller than 1 S/M. In some examples,the extinction coefficient is less than 0.1 at 550 nm. These materialsmay be selected for color tuning, e.g., to make the boundary of thediscontinuous layer invisible. Additional color tuning may be achievedby controlling the thickness of first dielectric layer 120 and seconddielectric layer 120. For example, first dielectric layer 120 and/orsecond dielectric layer 150 may have a thickness of 10 nm to 100 nm. Insome examples, first dielectric layer 120 and/or second dielectric layer150 allows for vacuum break during fabrication of energy-efficientsignal-transparent window assembly 100.

In some examples, each of first dielectric layer 120 and seconddielectric layer 150 is a uniform monolithic layer. Alternatively, oneor both first dielectric layer 120 and second dielectric layer 150 aremultilayered structures. At least one layer in these multilayeredstructures is formed using a dielectric material.

In some examples, conductive layer 130 is configured to provideIR-blocking for energy saving while allowing penetration ofsignal-carrying electromagnetic waves. Some examples of materialssuitable for conductive layer 130 include, but are not limited to,silver, silver alloys, copper, gold, ITO (indium tin oxide), and thelike. In some examples, the sheet resistance of conductive layer 130 issmaller than 100 Ohm/square. In some examples, the thickness ofconductive layer 130 is between 5 nanometers and 40 nanometers.

In some examples, conductive layer 130 is patterned or, morespecifically, formed by multiple disjoined structures 132. The size ofthese multiple disjoined structures 132 and the spacing between twoadjacent ones of multiple disjoined structures 132 are set by pattern.In some examples, the width (e.g., along the X-axis in FIG. 1A) of eachof multiple disjoined structures 132 is between about 0.05 millimetersand 5 millimeters or, more specifically, between about 0.1 millimetersand 2 millimeters. In the same or other examples, the spacing (e.g.,along the X-axis in FIG. 1A) between adjacent of two multiple disjoinedstructures 132 is between about 50 nanometers and 20 micrometers or,more specifically, between about 100 nanometers and 10 micrometers.These parameters define the transmissibility of energy-efficientsignal-transparent window assembly 100 to signal-carryingelectromagnetic waves.

In some examples, barrier layer 140 is used to protect conductive layer130 from the environment and degradation (e.g., to protect silver inconductive layer 130 from oxidation). The materials suitable for barrierlayer 140 include, but are not limited to metals or metal oxides, suchas NiCr, NiCrO_(x), TiO_(x), NiTiNb, and NiTiNbO_(x). In some examples,the thickness of barrier layer 140 is between about 1 nm and 15 nm.

As noted above, non-conductive spacers 180 are used for positioningspacer-interfacing stacks 172 and substrate-interfacing stacks 171 atdifferent levels thereby causing separations in conductive layer 130 toform multiple disjoined structures 132. In some examples, the height ofnon-conductive spacers 180 (e.g., along the X-axis in FIG. 1A) is atleast greater than the height of substrate-interfacing stacks 171 or,more specifically, at least three times greater. For example, the heightof non-conductive spacers 180 is between about 20 nanometers and 3000nanometers or, more specifically, between about 20 nanometers and 1000nanometers.

Non-conductive spacers 180 are positioned in openings 190, betweenadjacent pairs of substrate-interfacing stacks 171. It should be notedthat, in some examples, these openings 190 are formed due tonon-conductive spacers 180 being first positioned on window substrate110, e.g. while forming substrate-interfacing stacks 171 andspacer-interfacing stacks 172. Non-conductive spacers 180 prevent aportion of the deposited materials from reaching window substrate 110.As such, this portion of the deposited materials formsspacer-interfacing stacks 172.

In some examples, non-conductive spacers 180 comprise at least one orphotoresist, fibers, wires, various transparent materials, and otherlike materials and structures. For example, FIG. 1D illustrates anexample in which non-conductive spacers 180 are nanofibers arranged onwindow substrate 110. In some examples, non-conductive spacers 180comprise a positive photoresist, which is soluble in a photoresistdeveloper after being directly exposed.

In some examples, non-conductive spacers 180 have a cross-sectionalwidth of 0.1 micrometers to 20 micrometers is formed. In some examples,the electrical conductivity of non-conductive spacers 180 is less than1000 S/M (Siemens per meter) or, more specifically, less than 1 S/M. Insome examples, a patterned structure is transparent. For example, theextinction coefficient of patterned structure material is at leastsmaller than 0.3 at the visible region at 550 nm, specifically, smallthan 0.1 at 550 nm.

In some examples, non-conductive spacers 180 are spaced away fromsubstrate-interfacing stacks 171, e.g., as shown in FIG. 1A. As such,openings 190 comprise gaps, between non-conductive spacers 180 arespaced away from substrate-interfacing stacks 171.

In some examples, non-conductive spacers 180 have tapered shapes, e.g.,as shown in FIG. 1A. Specifically, each of non-conductive spacers 180has substrate-interfacing surface 181 and dielectric-interfacing surface182, opposite of substrate-interfacing surface 181. The width ofdielectric-interfacing surface 182 is larger than the width ofsubstrate-interfacing surface 181. In some examples, the differencebetween the width of dielectric-interfacing surface 182 and the width ofsubstrate-interfacing surface 181 is at least 100 nanometers or even atleast 200 nanometers. This taper helps to form the separation betweendisjoined structures 132 of conductive layer 130.

This taper of non-conductive spacers 180 may be achieved using varioustechniques. For example, non-conductive spacers 180 may be formed fromtwo different materials, which have different etch rates during theformation of non-conductive spacers 180 using photolithography.Specifically, each of non-conductive spacers 180 comprises spacer base188 and spacer head 189, e.g., as shown in FIG. 1C. Spacer base 188defines substrate-interfacing surface 181. Spacer head 189 definesdielectric-interfacing surface 182 and is formed from a material,different than spacer base 188, e.g., the etch rate of the materialforming spacer base 188 is greater than that forming spacer head 189.

In some examples, each of non-conductive spacers 180 is disposed betweentwo adjacent sidewalls 160, each extending to window substrate 110 andformed by at least one of barrier layer 140 and second dielectric layer150. Adjacent sidewalls 160 define opening 190 and face each other (andeach faces the corresponding one of non-conductive spacers 180).Furthermore, sidewalls 160 protect conductive layer 130 from theenvironment, e.g., when opening 190 has a gap between sidewalls 160 andnon-conductive spacers 180. In some examples, each of two adjacentsidewalls 160 is formed by both barrier layer 140 and second dielectriclayer 150. For example, sidewalls 160 are formed in situ whiledepositing barrier layer 140 and second dielectric layer 150.

Specifically, sidewalls 160 are formed by specifically tuning thedeposition processes of conductive layer 130, barrier layer 140, andsecond dielectric layer 150. In some examples, the sidewall thicknessesof barrier layer 140 and second dielectric layer 150 (identified as X₁and X₂ in FIG. 1B) can be defined as the horizontal measurementcorresponding to the centerline of conductive layer 130. To preventcorrosion and to improve durability, the sidewall thickness of barrierlayer 140 (identified as X₂) is at least about 1 nm, or even at least0.3 nm while the sidewall thickness of second dielectric layer 150(identified as X₂) is at least about 10 nm, or even at least about 2 nm.

Referring to FIG. 1B, each of two adjacent sidewalls 160 has sidewallsurface 161, facing the corresponding one of non-conductive spacers 180.Sidewall surface 161 is separated from conductive layer 130 by at least2 nanometers or, more specifically, by at least 3 nanometers as thehorizontal measurement corresponding to the centerline of conductivelayer 130. This distance may be defined as the thickness of sidewalls160.

In some examples, barrier layer 140 is patterned in addition to orinstead of conductive layer 130. For example, barrier layer 140 may bepatterned into a set of disjoined structures in a stack. When barrierlayer 140 is absent or very thin (e.g., 60% of the normal thickness inthe low-E structure), portions of conductive layer 130 may be exposed tothe environment in this gap area. These portions may oxidize and becomenon-conductive. These non-conductive portions may be operable as seconddielectric layer 150.

FIG. 1E illustrates another example of energy-efficientsignal-transparent window assembly 100, which comprises protective layer198. In this example, protective layer 198 conforms to the entiresurface of energy-efficient signal-transparent window assembly 100.Specifically, protective layer 198 extends over substrate-interfacingstack 171 and over the portion of window substrate 110 that is free fromsubstrate-interfacing stack 171, but also possibly covered over stack172 with or without non-conductive spacers 180. Furthermore, protectivelayer 198 forms adjacent sidewalls 160. The thickness of protectivelayer 198 may be from 10 nanometers to 10+ microns and even higher.

In some examples, energy-efficient signal-transparent window assembly100 is placed into an insulated glass unit (IGU) window, which featuresmultiple panes of glass, separated by an inert gas or vacuum, widelyused in buildings.

FIG. 2A is another example of energy-efficient signal-transparent windowassembly 100. Similar to the examples described above, in this example,energy-efficient signal-transparent window assembly 100 also compriseswindow substrate 110, first dielectric layer 120, conductive layer 130,barrier layer 140, and second dielectric layer 150. However, thisexample does not include any non-conductive spacers. These spacers, ifinitially present, were removed, e.g., during heat treating/tampering ofenergy-efficient signal-transparent window assembly 100. In other words,the example shown in FIG. 1A can be converted into the example shown inFIG. 2A.

Referring to FIG. 2A, first dielectric layer 120 is disposed over windowsubstrate 110. In more specific examples, first dielectric layer 120 isdisposed entirely on window substrate 110. In other words, no portion offirst dielectric layer 120 is disposed away from window substrate 110.Conductive layer 130 is disposed over first dielectric layer 120 suchthat first dielectric layer 120 is disposed between conductive layer 130and window substrate 110. Conductive layer 130 is formed by multipledisjoined structures 132 defined by openings 190, forming pattern 185.Various examples of pattern 185 are described below with reference toFIGS. 4A and 4B. Each of openings 190 is disposed between two adjacentsidewalls 160. Furthermore, barrier layer 140 is disposed overconductive layer 130 such that conductive layer 130 is disposed betweenfirst dielectric layer 120 and barrier layer 140. Finally, seconddielectric layer 150 is disposed over barrier layer 140 such thatbarrier layer 140 is positioned between second dielectric layer 150 andconductive layer 130. Overall, first dielectric layer 120, conductivelayer 130, barrier layer 140, and second dielectric layer 150 formsubstrate-interfacing stack 171 at least over a portion of windowsubstrate 110.

Unlike examples described above with reference to FIGS. 1A-1D,energy-efficient signal-transparent window assembly 100 in FIG. 2A doesnot include or is free from non-conductive spacers. In the example ofFIG. 2A, the separation between multiple disjoined structures 132 isachieved by openings 190, which remain unfilled. It should be noted thatenergy-efficient signal-transparent window assembly 100 in FIG. 2A maybe formed from any examples described above with reference to FIGS.1A-1D by removing non-conductive spacers from openings 190.

Referring to FIG. 2A, in some examples, each of two adjacent sidewalls160 extends to window substrate 110 and is formed by at least one ofbarrier layer 140 and second dielectric layer 150. In more specificexamples, each of two adjacent sidewalls 160 is formed by both barrierlayer 140 and second dielectric layer 150. Sidewalls 160 are used toprotect conductive layer 130 from the environment. More specifically,sidewalls 160 extend over the edge of conductive layer 130, which facesopenings 190, and blocks any access to conductive layer 130. As such,conductive layer 130 is protected from oxidation and other negativeeffects on the environment. For purposes of this disclosure, the term“sidewall” is referred to a portion of substrate-interfacing stacks 171(or a portion of spacer-interfacing stacks 172), extending over edge 131of conductive layer 130.

More specifically, each of two adjacent sidewalls 160 has sidewallsurface 161, facing another of two adjacent sidewalls 160. Thesesidewall surfaces 161 define, in part, opening 190. In some examples,sidewall surface 161 is separated from conductive layer 130 by at least2 nanometers or even at least 3 nanometers. This separation may bereferred to as a thickness of sidewalls 160 and, in some examples,represents a combined thickness of barrier layer 140 and seconddielectric layer 150. FIG. 2A illustrates the thickness of barrier layer140 as X₄ is at least about 1 nm, or even at least 0.3 nm and thethickness of second dielectric layer 150 as X₅ is at least about 10 nm,or even at least about 2 nm.

Referring to FIG. 2A, in some examples, a portion of window substrate110 between two adjacent sidewalls 160 is exposed. This portion may bereferred to as an exposed portion. In more specific examples, theexposed portion of window substrate 110, which extends between twoadjacent sidewalls 160, is planar and substantially intact. This featuredistinguishes energy-efficient signal-transparent window assembly 100 inFIG. 2A from conventional low-E windows, one example of which is shownin FIG. 2B. Specifically, FIG. 2B illustrates exposed portion 111 ofwindow substrate 110 being non-planar and having a high surfaceroughness. This non-planar type of exposed portion 111 is formed, e.g.,by laser scribing, which removes a portion of window substrate 110 whenforming opening 190. Furthermore, FIG. 2B illustrates conductive layer130 having exposed edge 131, which could be oxidized or otherwiseaffected by the environment.

Referring to FIG. 3 , in some examples, energy-efficientsignal-transparent window assembly 100 comprises multiple low-E stacks,formed on top of each other. Each low-E stack comprises first dielectriclayer 120, conductive layer 130, barrier layer 140, and seconddielectric layer 150. Two examples of such low-E stacks aresubstrate-interfacing stacks 171 and spacer-interfacing stacks 172, bothof which are described above. FIG. 3 also illustrates additional stacks173, positioned over substrate-interfacing stacks 171 andspacer-interfacing stacks 172. Similar to substrate-interfacing stacks171 and spacer-interfacing stacks 172, each of additional stacks 173comprises first dielectric layer 120, conductive layer 130, barrierlayer 140, and second dielectric layer 150. While FIG. 3 illustratesonly one additional stack 173 over each one of substrate-interfacingstacks 171 and spacer-interfacing stacks 172, one having ordinary skillin the art would understand that any number of stacks are within thescope.

FIGS. 4A and 4B illustrate top schematic views of two examples ofpatterns 185, formed by openings 190. As described above with referenceto FIG. 1A, openings 190 may have non-conductive spacers, positionedwithin openings, and each non-conductive spacer supportingspacer-interfacing stacks. Alternatively, openings 190 may be empty, asdescribed above with reference to FIG. 4B. Openings are surrounded bysubstrate-interfacing stacks 171.

Various types of patterns are within the scope. Specifically, FIG. 4Aillustrates a liner pattern, formed by parallel openings 190. FIG. 4Billustrates rectangular patterns, formed by two sets of parallelopenings 190, crossed each other, extending at a 90° angle relative toeach other, or other angles. This portion of energy-efficientsignal-transparent window assembly 100 may be referred to as patternedlow-E coating 102.

It should be noted that energy-efficient signal-transparent windowassembly 100 does not need to be covered by patterned low-E coating 102and some areas of energy-efficient signal-transparent window assembly100 may have un-patterned low-E coating 104 as, e.g., is schematicallyshown in FIG. 4C. In this example, energy-efficient signal-transparentwindow assembly 100 is still able to transmit signal-carryingelectromagnetic waves through patterned low-E coating 102, whileun-patterned low-E coating 104 may block these electromagnetic waves.

Processing Examples

FIG. 5 is a process flowchart corresponding to method 500 of forming anenergy-efficient signal-transparent window assembly 100, in accordancewith some examples.

Method 500 may commence with forming (block 510) pattern 185 ofnon-conductive spacers 180 on window substrate 110. For example, pattern185 of non-conductive spacers 180 may be formed using photolithographyas, e.g., is schematically shown in FIGS. 6A-6D. Specifically, FIG. 6Aillustrates a processing stage during which under-layer 610 is formed asa continuous coating on window substrate 110. FIG. 6B illustrates aprocessing stage during which photoresist layer 620 is formed overunder-layer 610. Photoresist layer 620 is also formed as a continuouscoating. Photoresist layer 620 may be formed from positive or negativephotoresist, which corresponds to whether the exposed portion ofphotoresist layer 620 is soluble or insoluble to a photoresistdeveloper. It should be noted that under-layer 610 is an optional layer.In some examples, photoresist layer 620 is formed directly on windowsubstrate 110. FIG. 6C illustrates a processing stage during whichphotoresist layer 620 is exposed, e.g., using photolithographic mask630. Finally, FIG. 6D illustrates a processing stage after etching andcleaning photoresist layer 620 and, if present, under-layer 610.Specifically, photoresist layer 620 is converted into spacer head 189,while under-layer 610 is converted into spacer base 188. The materialsof photoresist layer 620 and under-layer 610 may be selected such thatthe etching rate of under-layer 610 is faster than that of photoresistlayer 620. As a result, spacer base 188 has a smaller width than spacerhead 189. Collectively, spacer head 189 and spacer base 188 formnon-conductive spacers 180. While FIGS. 6A-6D illustrate an example inwhich two layers are used to form non-conductive spacers 180, one havingordinary skill in the art would understand that a single layer or morethan two layers may be used.

In some examples, the complexity and cost of large size lithographyequipment can be reduced by using a plurality of smaller sized modules(e.g., half size of the maximum substrate width in the production orsmaller). The lithography pattern from different modules can beoverlapped, and the light intensity non-uniformity crossing the wholelithography pattern area can be more than 20% calculated using theformula:

(MAX value−MIN value)/(2×AVERAGE value).

It should be noted that there is a tradeoff between the equipmentcomplexity/cost and the uniformity of the light intensity in thelithography equipment. Described are novel methods of using multiplemodule exposures, with a tolerance of >20% of non-uniformity of lightintensity, which can significantly reduce the lithography equipmentcost.

Integrating multiple modules in a lithography process may involveportions of energy-efficient signal-transparent window assembly 100 inwhich portions of low-E coating stack are not patterned. FIGS. 4C,described above, illustrates patterned portions 102 positioned withinnon-patterned portions 104. The size and relative areas of theseportions are selected based on the signal transmission requirements. Insome examples, the average width of non-patterned portions 104 issmaller than 50 centimeters or, more specifically, smaller than 10centimeters. In some examples, patterned portions 102 represent 20% or50% of the substrate total area with only 7 DB or 3 DB additional losseson the signal transmission. The lithography pattern area larger than 90%substrate area only introduces less than 1 DB additional loss on thecellphone transmission in comparing that of the whole substratepatterned. In this example with some areas without patterns, thepositive photoresist is used for the lithography. More specifically,areas without lithography patterns are cleaned out after the PRpost-development process, to leave clean glass surfaces for the rest ofthe glass coating processes.

Furthermore, in some examples, non-conductive spacers 180 have a taperedstructure, defined by an undercut. One such example is schematicallyshown in FIG. 6E. As described above, the undercut helps with formingthe separation between multiple disjoined structures 132 as furtherdescribed below.

FIGS. 7A-7D illustrate other examples of forming pattern 185 ofnon-conductive spacers 180. In some examples, non-conductive spacers 180are formed using nanoimprint lithography (NIL). In comparison tophotolithography, the NIL offers the benefits of low cost and highthroughput. For example, as shown in FIG. 7A, an imprint mask withphysical protrusions is mechanically pressed against a pre-coatedpatterning layer to mechanically deform it. Patterning material in thisarea with mechanical deformation is effectively removed. Alternatively,as shown in FIG. 8B, patterning materials are formed by imprint molding.Patterning material is transferred to the substrate in the area withphysical contact between molding and substrate.

Subsequent processing steps after NIL pattern generation aresubstantially the same or similar to processing steps used withphotolithography. To reduce equipment cost with NIL, multiple NILmodules of smaller size (e.g., half the size of substrate width or less)are combined to cover low-E glass width. This is similar to theaforementioned multiple photolithography module approaches.

Overall, pattern 185 of non-conductive spacers 180 may be formed usingmaterials extrusion, nozzle jetting, or indirectly deformationmechanically, such as using a mold, stamp, or by laser, UV source orelectron beam curing, or other heating source hardening, or combiningthose techniques.

In some examples, pattern 185 of non-conductive spacers 180 is formed byattaching fibers, wires, or other like structures to window substrate110. In some examples, a non-conductive material (e.g., plastics, glass,transparent polymers, transparent resins, photoresist) is coated andpatterned directly (e.g., using materials extrusion, nozzle jetting),indirectly (e.g., using a mold, a stamp, or by laser, UV source orelectron beam curing or other heating source hardening), or acombination of these techniques.

Returning to FIG. 5 , method 500 proceeds with depositing (block 520)stack 170 over window substrate 110 and non-conductive spacers 180. Asdescribed above, stack 170 comprises first dielectric layer 120,conductive layer 130, barrier layer 140, and second dielectric layer150. Each layer is formed in a separate operation using, e.g., physicalvapor deposition (PVD). FIGS. 8A-8D illustrate different stages duringthis stack-forming operation. As shown in FIG. 8B, conductive layer 130comprises multiple disjoined structures 132 defined by pattern 185 ofnon-conductive spacers 180. Disjoined structures 132 are formed due tonon-conductive spacers 180 protruding over the substrate.

In some examples, depositing stack 170 also comprises forming twoadjacent sidewalls 160 around each of non-conductive spacers 180 suchthat each of two adjacent sidewalls 160 around extends to windowsubstrate 110 and is formed by at least one of barrier layer 140 andsecond dielectric layer 150, which may be referred to as depositionextensions. Various ways of controlling the deposition extension (ofeach layer forming a stack in) the undercut area of the photoresist (PR)are within the scope. For example, increasing the pressure in asputtering deposition chamber makes deposition more isotropic or, inother words, less directional. Thus, there is more encroachment ofsputtered materials in the PR undercut region. For example, when thepressure is lower during the deposition of conductive layer 130 thanthat during the deposition of barrier layer 140 and also than thatduring the deposition of second dielectric layer 150, the edge sidewallof conductive layer 130 is covered by barrier layer 140 and seconddielectric layer 150. The higher the pressure difference, the thickersidewall protection is provided by each of barrier layer 140 and seconddielectric layer 150. For example, a low-pressure processing condition(such as 0.5˜2 milliTorr) is for the deposition of conductive layer 130.At a such low-pressure level, a very limited amount of material willreach the undercut region. On the other hand, a high-pressure condition(such as 3-300 milliTorr) is used for the deposition of barrier layer140 and second dielectric layer 150, providing more material into theundercut region. In some examples, additional and/or alternativetechniques are used to enhance the directional deposition of conductivelayer 130. One example is an ionized sputtering technique with highionization rate plasma from a special sputter source to enhance thesputtering directional feature. Another example is using a second biassource under the glass to enhance the directional sputter deposition.Additional examples include collimators for sputtering, and/orevaporation method that can enhance the direction deposition.

The sidewall protection of conductive layer 130 (with a barrier layerand a second dielectric layer) has demonstrated excellent environmentaland thermal durability. The environmental durability was tested bydipping a sample for one hour into a boiling water container. Thethermal durability was tested using 650° C. baking for 8 minutes. Therewere no noticeable defects under the microscope inspection.

These sidewall conductive layer protection designs and methods areapplicable to any stack and any number of layers in each stack. Bothhighly non-directional processes (e.g., high-pressure processes) anddirectional processes (e.g., low-pressure processes) are within thescope.

One issue of the undercut profile of a single-layer photoresist isinfluenced by the non-uniformity of the light intensity with lithographyequipment. There is a bi-layer method that minimizes this influence,where the bottom layer material having a dissolution rate in thedeveloper much less sensitive on light intensity than that of thephotoresist above the bottom materials, so the dissolution rate is moredependent on time and other processing parameters instead of exposinglight intensity. Thus, the undercut amount is more dependent on thephotoresist materials and less dependent on the light intensity. Assuch, a large non-uniformity of exposing light intensity has a verysmall influence on the undercut amount, so it can be acceptable in thisapplication.

Besides the pattern line sidewall profile, the top surface roughness canbe another factor. Further experiments on patterned structures with arectangular cross-sectional profile were studied to compare the effectsof oxygen plasma treatment. Oxygen plasma was generated using asputtering titanium gun with a pure oxygen flow process in a typicalvacuum sputtering system. After oxygen plasma treatment of the patternedstructures, the low-E coating stack was deposited on the top of thesestructures. After heating samples to 200° C. for 8 minutes inatmospheric conditions, the conductivity was different between thetreated samples and the controlled samples. Specifically, the low-E filmfrom the two sides of the patterned structure was not conductive for thetreated samples. However, it remains conductive for the controlledsamples (without oxygen plasma treatment). Without being restricted toany particular theory, this difference is attributed to the differencein the surface roughness of the top surface of a patterned structure.Specifically, the controlled samples' (without oxygen plasma treatment)top surface remained smooth (e.g., based on inspection). The surfaceroughness (Ra) was estimated to be 10 nm or below. However, treatedsamples (with oxygen plasma treatment) have demonstrated the formationof metal oxides on the top surface, which caused a significant increasein surface roughness to about Ra 0.1 micrometers to 10 micrometers. Inthis example, Ra is an arithmetic average value of absolute values ofthe profile height deviations from the mean line within the evaluationlength, such as 100 micrometers. The rough surface causes potentialdefects in low-E films (especially silver) at high temperaturesresulting in conductivity losses. However, a smooth surface allowsdeposition and subsequent thermal treatments of low-E films withoutsimilar defects such that the low-E films remain as good electricallyconductive. Thus, the surface roughness of the top surface of patternedstructures is another important factor impacting cellular signaltransmission.

In some examples, the height/thickness of the pattern line is between 20nm and 3000 nm with some being between 20 nm and 1000 nm. The desiredroughness upon oxygen treatment was achieved on a patterned photoresistwith a sputtering gun in a vacuum chamber. The top surface roughness wasestimated at approximately 10 nm-300 nm. Such roughness was likely dueto forming “peaks” and “valleys” from the area with and without metaloxide residues respectively. Specifically, metal oxide residues can be amicro-mask blocking the oxygen ashing, which results in peaks on the topsurfaces. On the other hand, the area without the “residue mask”protection, become “valleys” and were “ashed out” during the treatment.Low-E stacks were then deposited on these thin patterns. After heatingto 200° C. for 8 minutes at atmospheric conditions, the low-E film fromthe two sides of the pattern lines was no longer conductive. It shouldbe noted that in this experiment, the pattern lines were very thin(e.g., 20 nm˜1000 nm) and have a high surface roughness of the topsurfaces (Ra is estimated at 10 nm˜300 nm). The low-E coating depositedabove these pattern lines becomes non-conductive between the two sidesof the pattern line. It is expected that thin structures (e.g., lessthan 1000 nm in thickness) with rough top surfaces will show the sameperformance.

It should be noted that thin thicknesses (e.g., less than 3000 nm) ofpattern lines not only help with materials cost savings but also helpwith enhancing abrasion resistance, e.g., to avoid uneven coatingsurfaces between pattern lines and surrounding coatings.

Various methods of forming thin patterned lines (e.g., less than about3000 nm) with rough top surfaces (e.g, Ra of above 10 nm) are within thescope. One example is an oxygen plasma treatment, which forms a roughmetal oxide layer on the top surface of the patterned lines. Anotherexample involves using one or more special organic materials, doped with0.01% to 20% of one or more other metal elements or semi-conductorelements, followed by ashing through an oxygen plasma process. Someexamples of these metal/semiconductor elements include semi-conductorelements B, Si, Ge, and the main group I & II: Na, K, Rb, Mg, Ca Sr, Ba,main group III, IV, V: Al, Ga, In, Sn, Ti, Pb, Bi, and transition metalsTi, V, Cr, Mn, Fe Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Hf, Ta, W, Re, Ce,Dy, Eu, Gd, La, Nd, Pr, Sm, Sc, Tb. The benefit of the organic materialswith those dopants can generate particles as a seed mask during theoxygen ashing process, to form the “valleys” and “peaks” on the film, sothat the rough pattern can be generated.

In some examples, pattern lines are directly printed with roughmaterials by printing the solution and evaporating solvent with solutesremaining as patterned rough materials. Typical solvents are water,acetone, alcohol, etc.; the solute could be inorganic or organicmaterials, such as salts or base inorganic materials, of NaCl, Na₂CO₃,Na₂SO₄, Ca(OH)₂, NaOH, etc., or organic materials, such as polymerpowders.

Various examples of increasing the surface roughness of the top surfacesof patterned structures are within the scope. Some of these examplesinclude, but are not limited to, directly coating/printing materialswith high roughness or the materials being rough after specialtreatments. Furthermore, baking time, oxygen treatment, photoresistdeveloping conditions, photoresist organic materials may be specificallyselected to achieve the desired surface roughness.

Besides the sidewall profile and top surface roughness, the volume ofpattern line shrink after the high-temperature treatment can be anotherfactor for cell phone transmission. Patterned structures withrectangular cross-sections were tested using high-temperature treatmentin air, such as 650° C. for 8 minutes, which may be referred to as heattreatment. After the heat treatment, the patterned structures wereburned out if exposed to air, even when the pattern materials werecovered with low-E coating, the organic materials can partially bereactivated, and the pattern volume was shrunk dramatically before andafter heat treatment, more than 20% volume changed. The low-E film,located on the top of the patterned structure, became a very roughcoating (e.g., the surface roughness Ra of greater than 10 nm), and thelow-E coating was not conductive between the two sides of the patternedstructures. In this case, the initial photoresist is used to define theline pattern that makes the low-E coating film rough (such as Ra>10 nm).This enables a high roughness of the coating portion to make the low-Ecoating on both sides of the line non-conductive. Specifically, thesilver layer (of the low-E coating) composition increases the amount ofoxygen (O) elements, for example, more than 2% atomic, in comparison totheir corresponding silver layer at the neighbor coating on thesubstrate. Thus, for the large size (more than a square meter) coatingwith those pattern lines, the cell phone signal can penetrate thosecoating, after a glass temper process of high-temperature treatment atatmospheric conditions. Overall, the high-temperature treatment changesthe volume of photoresist patterns to make low-E stack coatings(disposed on the top of these patterns) become non-conductive from twosides of the photoresist line. As a result, low-E coatings become moretransmissive to cell phone signals.

In some examples, method 500 comprises depositing (block 530) one ormore additional stacks over stack 170, which is disposed over windowsubstrate 110 and non-conductive spacers 180

In some examples, method 500 comprises removing (block 540)non-conductive spacers 180 from energy-efficient signal-transparentwindow assembly 100. For example, energy-efficient signal-transparentwindow assembly 100 may be tempered (e.g., subjected to hightemperatures) turning non-conductive spacers 180 into volatile species,which are removed from the environment.

Experimental Results

Various tests have been conducted to characterize the energy-efficientsignal-transparent window assemblies, described above. The first testwas performed using Sample 1, which used a 2.2-millimeters thick glassas a window substrate. A first dielectric layer, deposited over thiswindow substrate, was formed from ZnSnO. A conductive layer was formedfrom silver-titanium alloy, while a barrier layer was formed fromtitanium. Finally, a second dielectric layer was also formed usingZnSnO. The overall coating size of this sample was 100 millimeters×60millimeters. The sample demonstrated a good sheet resistance of 7Ohm/square, which is equivalent to the emissivity of 0.08. Sample 1 didnot include any patterning of the conductive layer or any other layersand was used as a baseline reference.

IR blocking characteristics were tested using an IR lamp and alight-mill radiometer. Specifically, the radiometer vanes spin only whenIR radiation is present. Sample 1, described above, showed exceptionalIR blocking characteristics. When Sample 1 was inserted between the IRlamp and the radiometer, the vanes of the radiometer stopped spinningcompletely, which demonstrates effective IR blocking.

Electromagnetic wave transmission characteristics were tested using anon-metallic box, wrapped in aluminum foil and an opening of 95millimeters by 55 millimeters. The box simulates a building thatelectromagnetic waves cannot penetrate. Only the window in the boxallows electromagnetic wave penetration. Sample 1 was installed into theopening for testing. The signal source, used in this experiment, was a2.4 GHz router (using wavelengths of 125 millimeters). A phone, APPLE®IPHONE® 7, was used as a signal receiver. The phone was equipped with a“Wi-Fi-meter” software application to measure the Wi-Fi signalintensity, received by phone. A reference test was performed with anuncoated glass in the opening and demonstrated the signal strength of−36 dBm to −42 dBm. This signal strength represented a referencebaseline for the Wi-Fi signal in the whole test system, including theWi-Fi source, receiver iPhone, and the house simulator (the box wrappedby aluminum foils). When Sample 1 was placed into the opening, thesignal strength dropped from −67 dBm to −72 dBm. As such, two differentglass samples have shown about 30 dBm difference or around 1000 timesignal intensity reduction due to the low-E coating on the glass.

Sample 2 was prepared by depositing the first dielectric layer (alsoformed from ZnSnO) on the glass substrate. A thin wire with a gridpattern (80-micron diameter glass fiber) was placed over the firstdielectric layer to block portions of the first dielectric layer. Afteradding the wire, the assembly was reloaded into the vacuum chamber todeposit the first dielectric layer (also of ZnSnO), a conductive layer(of Silver Titanium alloy), a barrier layer (of titanium), and a seconddielectric layer (also of ZnSnO). The wire pattern was removed from theassembly and portions of later-deposited layers, extending over the wirepattern, were also removed. As such, a stack of the first dielectriclayer, the conductive layer, the barrier layer, and the seconddielectric layer becomes discontinuous. This wire removal forms gapsbetween discontinuous stack pieces. Another dielectric layer was thendeposited over these discontinuous stack pieces.

Sample 2 was inspected for various characteristics, in comparison toSample 1, which was a baseline sample without any patterning. The colorof Sample 2 was similar to that of Sample 1 (e.g., not distinguishablefor human eyes). The color similarity was attributed to the samestructure of Sample 1 and Sample 2, i.e., the same composition, order,and thickness of layers, except with a 2% of area difference at theboundary of discontinuous layers. However, Sample 2 had detectable linemarks at 90-degree using an unassisted human eye inspection angle andalso using a digital image. Both Sample 1 and Sample 2 had the samesheet resistance of 7 ohm/square, measured by a four-point probe,indicating the same emissivity. The IR blocking properties of Sample 2were the same as that of Sample 1. Specifically, when Sample 2 wasinserted between the IR lamp and the light mill radiometer, theradiometer vanes gradually stopped, indicating the IR blocking. Finally,the results of the “Wi-Fi” penetration test (aluminum foil-wrapped boxwith an opening) are shown in FIG. 9 . In comparison to Sample 1 (anun-patterned low-E coating), Sample 2 has shown a much stronger “Wi-Fi”signal reading of about −45 dBm to −50 dBm vs. −67 dBm to −72 dBm forSample 1. In other words, Sample 2 has shown about 20 dBm improvementover Sample 1 of a low-E coating or around 100-times signal strengthimprovements. The “Wi-Fi” penetration of Sample 2 is close to theuncoated than to Sample 1.

Another test sample, i.e., Sample 2A was prepared similarly to Sample 2.However, the grid pitch was increased to 12 mm for Sample 2A, incomparison to 6 mm for Sample 2. The test results were very similar forSample 2 and Sample 2A in terms of color, sheet resistance, IR blocking,and line mark visual ability. However, the “Wi-Fi” (2.4 GHz) penetrationwas about 5-10 dBm lower for Sample 2A in comparison to Sample 2. Assuch, a smaller pitch of gaps between the discontinuous stack piecesresults in better “Wi-Fi” signal penetration. This trend indicates thatthe “Wi-Fi” signal penetration can be further improved, if the gridpitch becomes smaller, such as 1 or 2 mm pitch. For high-frequencysignals, a small pitch may be used, e.g., 0.5 mm or less for a 5 GHzsignal. Pitches of 0.2 mm or less may be used for higher-frequencysignals.

Sample 2B was prepared in the same manner as Sample 2A. However, thepattern of Samples 2B was formed by parallel lines (e.g., as shown inFIG. 4A and described above). The pattern of Samples 2A was a squaregird (e.g., as shown in FIG. 4B and described above). Testing for thecolor, sheet resistance, IR blocking, and line mark visibility showedthe same results for Sample 2B and Sample 2A. A comparative “Wi-Fi”penetration test for Sample 2B and Sample 2A used three differentpolarization of radio waves: (1) an omnidirectional antenna “Wi-fi”router operating at 2.4 GHz; (2) a vertically-polarized router antenna;and (3) and a horizontally-polarized antenna. With the omnidirectionalantenna, the signal penetration results were similar for both samples(within a 5-dBm error bar). Switching to the vertically-polarizedantenna, a similar improvement (of about 20 dBm over the non-patternedconventional low-E coating) was observed in both Sample 2A and Sample2B. Finally, with the horizontally-polarized antenna, Sample 2B showed atransmission improvement of about 10 DBm over Sample 2A. Overall,parallel-line patterns perform similarly to cross-grid patterns withvertically-polarized and omnidirectional antennas, which are commonlyused today in communication networks (e.g., cellular networks). As such,parallel-line patterns can provide an economic solution for improvedcellular signal penetration.

Sample 3 was prepared similarly to Sample 2A but used 20-micrometermetal wires in Sample 3 in comparison to 80-micrometer glass fibers inSample 2A. The overall results were similar between these samples.However, the cross-grid pattern was even less visible in Sample 3although it was detectable during visual inspection.

Sample 4 used 10-micrometer metal wires but was otherwise the same asSample 2A and Sample 4. The overall results were similar with furtherimprovement toward lower detectability of grid lines. Overall, Sample 2,Sample 3, and Sample 4 indicate that thinner wires produce lessnoticeable patterns without compromising electromagnetic wavepenetration. As such, wires with a diameter of 20 micrometers or lessmay be used for adequate visual characteristics.

Sample 5 was the same as Sample 4, but the total thickness of theinitial dielectric layers was around 30 nanometers in Sample 5 or halfof that in Sample 4. The overall results were similar for Sample 5 andSample 4 in terms of sheet resistance, IR blocking, and cellular signalpenetration. However, the cross-grid pattern in Sample 5 was notdetectable under a normal inspection at a 90° angle, which was animprovement over Sample 4. Overall, the dielectric thickness on eachside of the conductive layer can be selected to improve the reflectiveand color transmittance. It should be noted that the line markvisibility was due to the color difference between the bulk portion andthe discontinued portion. Sample 6 was prepared using a pattern formedusing 80-micrometer glass fibers, attached to a clean glass substrateusing a KAPTON(R) tape.

Thereafter, a vacuum deposition process is the same as for Sample 1described above. Examining the (1) to (5) steps, the results are verysimilar to Sample #2A in terms of the color, sheet resistance, and IRblocking, but significantly improving the cellular signal penetration,which is significantly different from the low-E Sample #1; however, theline pattern lines are clearly visible.

Sample 7 is similar to Sample 6 but the 80-micrometer glass fiber wasreplaced with a 10-micrometer metal wire. The performance results ofSample 7 are similar to that of Sample 6, upon the color, sheetresistance, IR blocking, and cellular signal penetrating. However, thepattern in Sample 7 is still visible, although improved visibility dueto the wire size being reduced from 80 micrometers to 10 micrometers.

After analyzing the reasons for the pattern visibility issue, it hasbeen found a solution for the pattern visibility for Sample 7. Thepattern visibility in Sample 7 is believed to be due to (1) the wirebeing non-transparent (made from metal, instead of transparent glassfiber), and (2) the dielectric thickness being not optimized to make thereflective color matching between bulk and pattern lines. If a20-micrometer or thinner glass fiber (transparent materials) is applied,and if the dielectric thickness is optimized, the invisible line markcan be achieved during the inspection at a 90° angle.

Pattern lines can be tested for electrical conductivity, which isanother method for evaluating the signal transmission of a structure. Ifthe patterned structure is not conductive, then this low-E coating istransmissive to cellular signals. Thus, the electrical resistance of apatterned structure, which can be measured (e.g., by a multimeter), is agood indicator of cellular signal transmission of an assembly comprisingthis patterned structure.

Conventional pattern lines, which are formed using conventionallithographic equipment and techniques, e.g., without additionaltreatment, are not sufficient for cell phone signal transmission.Specifically, these conventional pattern lines do not have an undercut,unlike the structure shown in FIG. 6E. Without an undercut, a low-Estuck, which is formed over pattern lines, does not form separately in aconductive layer. As such, the conductive layer remains continuous (asopposed to being broken down into multiple disjoined structures), whichis evidenced by high conductivity. For example, a test was performed tocompare conventional pattern lines (without an undercut) to test lines(with an undercut). A low-E stuck formed over the conventional patternlines demonstrated resistance of less than 50 Ohm. A low-E stuck formedover the pattern lines with undercuts demonstrated resistance of morethan 20 Mega Ohms. The undercut amount was more than 100 nm, which isdefined as the average amount of difference along the pattern line,between the line width at the top and the smallest line width at anyheight from the bottom to the top. If in the photoresist cross-sectionpicture, the line that connected the edge of the top corner to theundercut bottom corner, can form an angle to the substrate surface, asshown in FIG. 6E, and this angle can be smaller than 88° (degrees) or atleast smaller than 80° (degree).

CONCLUSION

Although the foregoing concepts have been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. It should be noted that there are many alternative waysof implementing processes, systems, and apparatus. Accordingly, thepresent examples are to be considered illustrative and not restrictive.

What is claimed is:
 1. An energy-efficient signal-transparent windowassembly comprising: a window substrate; a first dielectric layer,disposed over the window substrate; a conductive layer, disposed overthe first dielectric layer such that the first dielectric layer isdisposed between the conductive layer and the window substrate, whereinthe conductive layer is formed by multiple disjoined structures definedand separated by openings forming a pattern; a barrier layer, disposedover the conductive layer such that the conductive layer is disposedbetween the first dielectric layer and the barrier layer, wherein thebarrier layer comprises nickel or titanium; and a second dielectriclayer, disposed over the barrier layer such that the barrier layer ispositioned between the second dielectric layer and the conductive layer,wherein at least one of the barrier layer and the second dielectriclayer forms sidewalls blocking and separating each of the multipledisjoined structures of the conductive layer from the openings formingthe pattern, wherein each of the openings is disposed between twoadjacent ones of the sidewalls, and wherein each of the first dielectriclayer and the second dielectric layer is either a uniform monolithicstructure or a multi-layered structure.
 2. The energy-efficientsignal-transparent window assembly of claim 1, wherein a portion of thewindow substrate between the two adjacent ones of the sidewalls isexposed.
 3. The energy-efficient signal-transparent window assembly ofclaim 1, wherein a portion of the window substrate between the twoadjacent ones of the sidewalls is planar and substantially intact. 4.The energy-efficient signal-transparent window assembly of claim 1,wherein each of the sidewalls extends over edges of the conductivelayer.
 5. The energy-efficient signal-transparent window assembly ofclaim 1, wherein one component of the sidewalls is formed by the barrierlayer.
 6. The energy-efficient signal-transparent window assembly ofclaim 1, wherein one component of the sidewalls is formed by the seconddielectric layer.
 7. The energy-efficient signal-transparent windowassembly of claim 1, wherein two components of the sidewalls are formedby both the barrier layer and the second dielectric layer.
 8. Theenergy-efficient signal-transparent window assembly of claim 1, whereinthe barrier layer has a thickness, separate from the conductive layer ofat least 0.3 nanometers.
 9. The energy-efficient signal-transparentwindow assembly of claim 1, wherein the second dielectric layer has athickness, separate from the conductive layer, of at least 2 nanometers.10. The energy-efficient signal-transparent window assembly of claim 1,wherein: the energy-efficient signal-transparent window assemblycomprises patterned portions and non-patterned portions, the patternedportions are defined by the conductive layer being formed by themultiple disjoined structures defined and separated by the openings, thenon-patterned portions are defined by the conductive layer beingcontinuous between adjacent ones of the patterned portions, and thenon-patterned portions has a width, at least in one direction, of lessthan 50 centimeters.
 11. The energy-efficient signal-transparent windowassembly of claim 1, wherein: the energy-efficient signal-transparentwindow assembly comprises patterned portions and non-patterned portions,the patterned portions are defined by the conductive layer being formedby the multiple disjoined structures defined and separated by theopenings, the non-patterned portions are defined by the conductive layerbeing continuous between adjacent ones of the patterned portions, and anarea of the non-patterned portions is at least 20% of a total area ofthe window substrate.
 12. The energy-efficient signal-transparent windowassembly of claim 1, wherein: the multiple disjoined structures aredefined and separated by openings forming a pattern, and each themultiple disjoined structures has a width of between 0.05 millimetersand 5 millimeters.
 13. The energy-efficient signal-transparent windowassembly of claim 12, wherein each of the openings has a width ofbetween 0.1 micrometers to 20 micrometers.
 14. The energy-efficientsignal-transparent window assembly of claim 12, wherein the openingsform a pattern of parallel lines.
 15. The energy-efficientsignal-transparent window assembly of claim 1, further comprising aprotection layer disposed over the window substrate, the sidewalls, anda stack formed by the first dielectric layer, the conductive layer, thebarrier layer, and the second dielectric layer.
 16. The energy-efficientsignal-transparent window assembly of claim 15, where the protectionlayer has a thickness of greater than 10 nanometers.
 17. Theenergy-efficient signal-transparent window assembly of claim 1, wherethe barrier layer further comprises at least one of chromium andniobium.
 18. The energy-efficient signal-transparent window assembly ofclaim 1, where the window substrate comprises glass or plastic.
 19. Theenergy-efficient signal-transparent window assembly of claim 1, wherethe first dielectric layer comprises multiplayer structures, forming astack and having different compositions.
 20. The energy-efficientsignal-transparent window assembly of claim 1, where the seconddielectric layer comprises multiplayer structures, forming a stack andhaving different compositions.